1. Field of the Invention
The present invention relates generally to a semiconductor structure and fabrication method thereof, and more specifically, to a semiconductor structure and fabrication method thereof, which forms a nitrogen-containing layer on the contact surface of an isolation structure and an epitaxial layer.
2. Description of the Prior Art
With increasing miniaturization of semiconductor devices, various Fin-shaped field effect transistor (FinFET) devices have been developed. The Fin-shaped field effect transistor (FinFET) is advantageous for the following reasons. First, manufacturing processes of Fin-shaped field effect transistor (FinFET) devices can be integrated into traditional logic device processes, and thus are more compatible. In addition, since the three-dimensional structure of the FinFET increases the overlapping area between the gate and the substrate, the channel region is more effectively controlled. This therefore reduces drain-induced barrier lowering (DIBL) effect and short channel effect. Moreover, the channel region is longer for the same gate length. Therefore, current between the source and the drain is increased.
Although the Fin-shaped field effect transistor (FinFET) is advantageous for many reasons, performance still needs to be improved. For instance, the epitaxial layers in the Fin-shaped field effect transistor (FinFET) often cover the fin-shaped structures used as source/drain regions to increase the total volume of the source/drain regions. However, as the epitaxial layers are selectively deposited and cover the surface of the fin-shaped structures, the bottom surfaces of the epitaxial layers make contact with the isolation structure below. The different materials of the epitaxial layers and the isolation structure cause mutual repulsion, resulting in a 54.8° launch angle of the epitaxial layers relative to the isolation structure, such that the epitaxial layers and the isolation structure cannot form a complete connection to each other. As a result, owing to each of these epitaxial layers growing upward with an oblique angle relative to the isolation structure, the total volume of each epitaxial layer is limited. Further, sequentially formed silicide is not easy to attach to the epitaxial layers.